With the development of technologies in recent years, downsizing and high density mounting of semiconductor devices are underway, and heat, generated when such semiconductor devices are operated, is becoming problematic. When semiconductor devices become hot due to heat generation, performance deterioration and thermal destruction or the like may be more likely to occur, and therefore a technique for preventing such a problem is required.
Examples of techniques for preventing performance deterioration and thermal destruction or the like include a method of detecting temperature of a semiconductor device using a temperature measuring device and changing the operation of the semiconductor device to a power-saving mode when the temperature exceeds a predetermined temperature, a method of controlling performance of a cooling device for cooling a semiconductor device according to the temperature of the semiconductor device or a method combining those methods.
Configurations of a temperature measuring device are described, for example, in Japanese Laid-Open Patent Application No. 2007-281139A (hereinafter referred to as “Patent Document 1”), Japanese Laid-Open Patent Application No. 2004-219410A (hereinafter referred to as “Patent Document 2”) and Japanese Laid-Open Patent Application No. 2007-067275A (hereinafter referred to as “Patent Document 3”). Patent Documents 1 to 3 describe configuration examples of temperature measuring device using a semiconductor device whose characteristics vary depending on temperature and which is used as a temperature sensor.
Patent Document 1 describes a temperature control system which saves an output value (set value) of a temperature detecting section corresponding to a predetermined set temperature beforehand and starts a cooling operation when the output value of the temperature detecting section exceeds the set value.
Furthermore, Patent Document 2 describes a configuration which creates a lookup table that associates output values of a temperature sensor with absolute temperatures beforehand and converts an output value of the temperature sensor to information on an absolute temperature by looking up the lookup table.
Patent Document 3 describes a configuration which creates a plurality of temperature sensors having different threshold voltage temperature characteristics using a known temperature characteristic of a semiconductor device used as a temperature sensor, compares an output value of each temperature sensor with a reference voltage and thereby acquires information on an absolute temperature.
However, the temperature measuring devices disclosed in above described Patent Documents 1 to 3 have the following problems.
Since the temperature measuring device described in Patent Document 1 adopts a configuration which determines whether or not the output value of the temperature detecting section has exceeded a set value, it is necessary to sweep the set value to obtain an absolute temperature. Therefore, the circuit scale necessary to obtain the absolute temperature increases and the processing procedure also becomes more complicated.
The temperature measuring device described in Patent Document 2 converts the output value of a temperature sensor to an absolute temperature by looking up the lookup table, and therefore an absolute temperature corresponding to the output value of a temperature sensor that is not stored in the lookup table cannot be obtained. Furthermore, since a large amount of data needs to be stored in the lookup table to detect absolute temperatures with high definition, the amount of memory capacity that is provided with the lookup table need to be increases. There can also be a method which reduces information stored in the lookup table by calculating a corresponding absolute temperature from the output value of a temperature sensor not found in the lookup table using a linear equation or non-linear equation. However, the accuracy of a conversion expression for converting the output value of the temperature sensor to the absolute temperature becomes problematic and an accurate temperature can not always be detected.
The temperature measuring device described in Patent Document 3 determines parameters of each semiconductor device used as a temperature sensor based on a known temperature characteristic, but a variation in the characteristic of the semiconductor device, caused by the manufacturing process, is not taken into consideration. Therefore, there is a problem in that the measuring accuracy varies.